WIND 
AND  WEATHER 

ALEXANDER  McADIE 


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WIND 

•  ;  ..'  ^$0  ...     AND      '         • 

WEATHER 

BY 

ALEXANDER  McADIE 

A.  Lawrence  Rotch  Professor  of  Meteorology,  Harvard 

University  and  Director  of  the  Blue  Hill 

Observatory 


THE  MACMILLAN  COMPANY 

1922 

All  rights  reserved 


Copyright,  19  ", 
By  ALEXANDER  McADIE. 


Set  up  and  electrotyped.    Published  November, 


LIST  OF  ILLUSTRATIONS 


HOW  THE  WIND  RUFFLES  THE  TOP 

OF  A  FOG  BANK Frontispiece 

PAGE 

FIG.  I .  THE  TOWER  OF  THE  WINDS IJ 

"  2.  BOREAS— THE  NORTH  WIND  19 

"  3.  KAIKIAS THE  NORTHEAST  WIND  ...23 

"  4.  APHELIOTES THE  EAST  WIND 29 

5.  EUROS THE  SOUTHEAST  WIND 33 

"  6.  NOTOS THE  SOUTH  WIND 37 

7.  LIPS THE  SOUTHWEST  WIND 4! 

"  8.  ALL  STORMS  LEAD  TO  NEW  ENGLAND  .  45 

"  9.  ZEPHYROS THE  WEST  WIND  49 

IO.  PATHS  OF  HIGH  AND  LOW,  JANUARY, 

i922 55 

"      II.  SKIRON THE  NORTHWEST  WIND.  ...  59 

12.  THE  IDEALIZED  STORM 63 

"      13.  TURNING  OF  WIND  WITH  ALTITUDE     ..  6j 

14.  VELOCITY    OF    SUMMER    AND    WINTER 

WINDS  73 

15.  BLUE  HILL  OBSERVATORY  IN  AN  ICE 

STORM     79 


500823 


WIND    AND   WEATHER 


WIND   AND  WEATHER 


THE  TOWER  OF  THE  WINDS 

In  Athens  on  the  north  side  and  near 
the  base  of  the  hill  on  which  the  upper 
city — the  Acropolis — is  built,  there  is 
a  small  temple  still  standing,  altho  its 
walls  were  completed  twenty-two  cen- 
turies ago.  It  is  known  as  the  Tower  of 
the  Winds;  but  as  a  matter  of  fact,  the 
citizens  of  Athens  used  it  to  tell  the 
hour  of  the  day  and  the  seasonal  posi- 
tion of  the  sun.  It  was  a  public  time- 
piece. It  served  as  a  huge  sun  dial. 
Water  from  a  spring  on  the  hillside 
filled  the  basins  of  a  water  clock  in  the 
basement  of  the  Tower.  And  so, 
whether  the  day  was  clear  or  cloudy  the 
measure  of  the  outflow  of  water  indi- 
cated the  time  elapsed.  Also  there  were 
markings  or  dials  on  each  of  the  eight 


WIND        AND        WEATHER 

walls  of  the  temple,  and  the  position  of 
the  shadow  of  a  marker  indicated  the 
seasonal  advance  or  retreat  of  the  sun  as 
it  moved  north  from  the  time  of  the 
winter  solstice  and  then  south  after  the 
summer  solstice. 

The  sun  is  not  an  accurate  time  keeper 
and  no  one  to-day  runs  his  business  or 
keeps  engagements  on  sun  time.  But 
the  old  Athenians  were  quite  content  to 
do  so;  and  their  Tower  served  excellently 
for  their  needs.  And  they  did  what  we 
moderns  fail  to  do,  namely,  give  dis- 
tinctive names  to  the  winds.  They 
represented  figuratively  the  character- 
istics of  the  weather  as  the  wind  blew 
from  each  of  the  eight  cardinal  direc- 
tions. 

The  allegorical  figures  of  the  winds 
used  in  this  little  book  are  reproduc- 
tions of  the  eight  bas-reliefs  in  the  li- 
brary of  the  Blue  Hill  Observatory, 
placed  there  by  the  late  Professor  A. 

[12] 


FIG.  i .    THE  TOWER  OF  THE  WINDS 

Erected  in  Athens,  on  the  north  side  of  the  Acropolis, 

B.C.  150 


WIND        AND        WEATHER 

Lawrence    Rotch.  They    are    copied 

from   the   frieze  of  the  Tower  of  the 
Winds  at  Athens. 


THE  NAMES  OF  THE  WINDS 

Boreas,  the  north  wind,  is  perhaps  the 
most  important  of  all  winds.  At 
Athens  this  a  cold,  boisterous  wind  from 
the  mountains  of  Thrace.  The  noise  of 
the  gusts  is  so  loud  that  the  Greek 
sculptor  symbolized  the  tumult  by  plac- 
ing a  conch  shell  in  the  mouth  of  Boreas. 
His  modern  namesake,  the  Bora  of  the 
Adriatic,  is  the  same  noisy,  blustering, 
cold  wind-rush  from  the  north. 

The  northeast  wind  Kaikias  is  a  trifle 
more  pleasant  looking  than  Boreas,  but 
still  not  much  to  brag  about.  Master 
of  the  squall  and  thunderstorm,  he  car- 
ries in  his  shield  an  ample  supply  of  hail- 
stones, ready  to  spill  them  on  defense- 
less humanity.  He  might  well  serve  as 

[15] 


WIND        AND        WEATHER 

the  patron  saint  of  air  raiders  dropping 
their  bombs  on  helpless  humans  below. 

Apheliotes,  the  east  wind,  is  a  grace- 
ful youth,  with  arms  full  of  flowers, 
fruit  and  wheat.  Naturally  this  was  a 
favorite  wind,  blowing  in  from  the  sea, 
with  frequent  light  showers.  Some  of 
us  who  dwell  on  the  Atlantic  Coast,  in 
more  northern  latitudes  than  Athens,  do 
not  always  regard  with  favor  the  east 
wind,  associating  it  with  chilly,  damp 
and  sombre  weather.  Yet  it  is  the  har- 
binger of  good — tempering  the  cold  of 
winter  and  the  heat. of  summer.  It  is  an 
angel  of  mercy  in  mid-summer  when 
the  temperature  is  above  the  nineties 
and  there  is  no  air  stirring.  Then  it  is, 
that  we  all  welcome  the  refreshing  wind 
from  the  sea. 

Euros,  the  southeast  wind,  and  neigh- 
bor to  Apheliotes,  is  a  cross  old  fellow, 
intent  on  the  business  of  cloud  making. 
He  alone  of  all  the  winds  carries  nothing 

[16] 


WIND        AND        WEATHER 

in  his  hands.  In  the  New  Testament  he 
becomes  Euroclydon,  wind  of  the  waves. 
He  is  no  friend  of  the  sailor;  and  the  sea- 
sick traveler  prays  to  be  rid  of  his  com- 
pany. 

The  figure  on  the  south  face  of  the 
tower,  Notos,  is  the  master  of  the 
warm  rain.  He  carries  with  him  a 
water  jar  which  has  just  been  emptied. 
Compare  his  light  flowing  robes  and 
half-clad  neck  and  arms  with  the  close 
fitting  jacket  of  old  Boreas.  At  his 
shrine,  hydraulic  engineers  well  might 
worship. 

Next,  the  Mariner's  wind,  Lips,  the 
southwest  favoring  breeze  bringing  the 
ships  speedily  into  harbor;  yes,  into  that 
Piraeus,  famed  in  classic  history.  In- 
cidentally it  is  the  southwest  wind  which 
differentiates  the  climate  of  Great  Brit- 
ain from  that  of  Labrador.  This  wind 
makes  Northwest  Europe  habitable; 
while  on  the  other  side  of  the  Atlantic, 

[17] 


WIND        AND        WEATHER 

in  similar  latitudes,  but  under  the  in- 
fluence of  prevailing  northwest  winds, 
we  find  Labrador — a  section  certainly 
misnamed,  for  it  is  not  the  abode  of 
farmers,  as  the  name  implies — but  barren 
and  bleak.  What  a  difference  it  would 
make  thruout  this  region  if  the  Gulf 
Stream  continued  north,  close  to  the 
shore,  and  the  prevailing  winds  were 
from  the  east.  Our  North  Atlantic 
Coast  would  then  be  the  land  of  zephyrs , 
using  the  word  in  the  sense  of  pleasant, 
gentle  winds. 

Zephyros,  the  west  wind,  is  repre- 
sented as  a  graceful  youth,  scantily  clad, 
with  his  arms  filled  with  flowers.  In 
Greece  this  wind  traversed  the  Ionian 
Sea  and  the  Gulf  of  Corinth  before  reach- 
ing Athens.  It  is  quite  unlike  our  west 
wind  which  blows  across  a  continent,  and 
is  continuously  robbed  of  its  water 
vapor  on  the  long  passage.  The  Ionian 
wind  is  pleasantly  moist  and  refreshing. 

[it] 


WIND        AND        WEATHER 

Last  of  all,  but  by  no  means  least  im- 
portant, is  Skiron,  lord  of  gusty  north- 
west gales.  Freezing  in  winter,  parch- 
ing in  summer,  he  carries  with  him  a 
brazen  fire  basket  and  spills  a  generous 
stream  of  hot  air  on  all  below.  '  His 
husky  Highness  might  not  inappropri- 
ately adorn  legislative  halls  and  editorial 
sanctums.  He  would  displace  the  blind- 
folded lady  holding  scales  very  much 
out  of  balance.  Think  of  the  deep  signifi- 
cance of  his  presence. 

In  our  country  the  northwest  is  of 
all  winds,  except  the  west,  most  per- 
sistent. For  1600  hours  in  a  year,  this 
wind  is  with  us.  Joining  forces  with  the 
west  wind,  these  directions  prevail  one 
third  of  the  time.  These  northwest- 
west  winds  also  have  the  greatest  speed 
and  gustiness.  The  climate  of  the 
United  States  is  essentially  determined 
by  the  prevalence  of  the  north,  north- 
west and  west  winds. 


*     * 


FORECASTING    THE    WEATHER 

In  old  days,  the  haruspices  (for  this  is 
what  the  Romans  called  weather  men 
in  the  days  of  Caesar)  proclaimed  the 
will  of  the  gods  by  consulting  the  en- 
trails of  some  freshly  killed  animal. 
Evidently  these  haruspices  did  not  al- 
ways make  correct  forecasts;  for  there 
were  some  Romans  who  openly  ques- 
tioned their  worth.  Cato,  the  Censor, 
is  on  record  as  saying  "that  he  wondered 
how  one  haruspex  could  look  another  in 
the  face  without  laughing!" 

The  modern  professional  forecaster 
would  scorn  to  consult  the  entrails. 
There  are  however  many  amateur  fore- 
casters who  foretell  weather  by  their 
aches  and  rheumatic  pains.  Probably 
there  is  a  high  correlation  factor  between 
body  sensations  and  dampness;  and  some 
individuals  are  quite  sensitive  to  changes 
in  both  relative  and  absolute  humidity. 
[22] 


WIND        AND        WEATHER 

This,  however,  does  not  always  mean 
that  a  storm  is  approaching.  Humidity 
or  dampness  is  only  one  factor  and  may 
be  quite  local,  whereas  most  storms  are 
wide-spread. 

*     *     *     * 

THE  WEATHER  MAP 

The  official  forecaster  consults  a  daily 
weather  map  and  certain  auxiliary  maps 
which  show  changes  in  pressure  and 
temperature  for  twelve  hours  or  more. 
He  examines  closely  the  contours  of 
pressure  as  shown  on  the  map.  The 
synoptic  map,  as  it  is  called,  because  it 
is  a  glance  at  weather  conditions  over  a 
large  area  at  one  and  the  same  moment, 
is  a  map  on  which  are  plotted  pressure, 
temperature,  wind  direction,  velocity 
and  rainfall.  The  lines  of  equal  pressure 
or  isobars  generally  curve  and  inclose 
what  is  known  as  a  cyclonic  centre,  or 
depression  or  LOW.  The  arrows  point 

[25] 


WIND        AND        WEATHER 

in,  but  not  exactly  toward  the  centre  of 
the  depression. 

On  the  map  there  will  probably  appear 
also  an  area  of  high  pressure  where  the 
surface  air  flows  leisurely  outward  and 
away  from  the  place  of  highest  pressure. 
Such  an  area  is  called  an  anticyclone, 
a  word  first  used  by  Sir  Francis  Galton 
in  1863  to  designate  not  only  high  pres- 
sure, but  general  flow  of  the  air  in  a 
reversed  or  opposite  direction  to  that  of 
the  low  area  or  cyclone.  The  word  cy- 
clone was  first  used  by  Piddington  in 
1843  in  describing  the  flow  of  the  air  in 
the  typhoons  of  the  East  Indian  Seas. 
It  is  from  the  Greek  and  literally  means 
the  coils  of  a  serpent.  The  word  cyclone 
must  possess  some  special  merit  in  the 
minds  of  journalists  for  it  is  quite  com- 
monly misused  for  tornado  in  descrip- 
tions of  the  smaller  and  more  destructive 
storm. 


[26] 


THE  LOW 

Cyclone  is  simply  the  generic  name 
for  a  large  rotating  air  mass.  It  is  a  baro- 
metric depression  or  LOW  and  is  Char- 
acterized by  a  flow  of  air  inward  and 
around  a  moving  centre.  The  air  circu- 
lation is  counter-clockwise  in  the  north- 
ern hemisphere  and  clockwise  in  the 
south. 

Perhaps  if  the  earth  stopped  rotating 
and  there  was  no  planetary  circulation, 
with  the  great  west-moving  trades  and 
east-moving  "westerlies,"  the  arrows  on 
the  weather  map  would  all  point  directly 
toward  the  centre  of  the  LOW;  but,  as 
things  are,  there  are  some  very  good  rea- 
sons why  air  can  not  move  directly  into 
a  LOW,  that  is  at  right  angles  to  the 
isobars. 

Moreover,  the  weather  map  does  not 
indicate  the  true  flow  of  the  air,  for  ob- 
servations of  the  wind  made  at  the 

[27] 


WIND        AND        WEATHER 

ground  tell  only  a  part  of  the  story  of 
the  balance  which  the  flowing  air  must 
maintain  under  the  action  of  various 
forces,  such  as  gravitation,  rotational 
deflection,  centrifugal  tendency,  and 
the  various  expansion  and  compression 
forces. 

The  winds  near  the  ground  are  modi- 
fied both  in  velocity  and  direction  by 
friction.  The  free  flow  is  often  inter- 
fered with  by  topography. 


THE  TRUE  AIR  FLOW 

One  must  rise  above  the  ground  some 
distance  to  get  the  true  air  flow,  or  what 
is  known  as  the  gradient  wind,  the  flow 
which  balances  the  gradient,  i.e.  a  flow 
along  the  isobars.  The  gradient  veloc- 
ity is  found  about  300  metres  above  the 
ground,  and  the  gradient  direction  a 
little  higher.  The  lower  clouds  as  a  rule 
[28] 


WIND        AND        WEATHER 

indicate  true  wind  values  very  well;  and 
so,  it  is  desirable  in  studying  winds  to 
use  cloud  directions  and  velocities  rather 
than  surface  values.  In  cloud  work  a 
nephoscope  is  essential.  The  unaided 
eye,  unless  properly  shielded,  suffers 
from  the  glare  of  a  sunlit  sky;  and  more- 
over, there  are  no  fixed  points  or  refer- 
ences. A  black  mirror,  with  suitable 
sighting  rods  and  measuring  devices,  en- 
ables an  observer  to  follow  the  cloud, 
estimate  its  height  and  determine  with 
accuracy  the  direction  from  which  it  is 
moving.  There  is  an  average  difference 
of  30  degrees  between  the  cloud  direc- 
tion and  the  surface  wind;  the  upper  di- 
rection being  more  to  the  right.  At 
times  the  directions  may  be  opposite. 

It  may  seem  surprising  but  few  of  us, 
except  at  sunrise  and  sunset,  really  see 
what  is  going  on  in  cloud  land. 

Some    meteorologists    hold    that    the 
[31] 


WIND        AND        WEATHER 

circulation  of  air  3000  to  5000  metres 
above  the  ground  controls  the  path  and 
perhaps  the  intensity  of  storms.  It  is 
therefore  important  to  know  something 
of  the  flow  at  high  levels  if  we  would  im- 
prove the  forecasts. 

*     *     *     * 
LIMITATIONS  OF  MAP 

The  weather  map  fails  to  indicate 
what  shifts  of  direction  and  changes  in 
velocity  are  likely  to  occur.  The  fore- 
caster tries  to  anticipate  these,  but  he 
bases  his  conclusions  chiefly  upon  an  ex- 
pected movement  of  the  low  area;  using 
the  accumulated  records  of  the  paths  of 
past  storms.  But  each  storm  is  in  reality 
a  law  unto  itself;  and  while  we  know 
something  of  the  relations  between  pres- 
sure and  flow  of  the  air;  as  yet  we  know 
very  little  about  the  relations  of  wind 
and  weather.  The  problem  is  compli- 
[32] 


WIND        AND        WEATHER 

cated  by  the  behavior  of  the  load  of 
water  vapor. 

The  Chief  Forecaster  of  one  of  the 
great  national  weather  services  recently 
wrote: 

"Despite  the  fact  that  maps  have 
now  been  drawn  day  by  day  for  over 
half  a  century,  we  may  safely  say  that 
no  two  maps  have  been  identical." 
It    is    perhaps    unfortunate    that    so 
much  attention  has  been  given  to  the 
cyclone  or  depression  or  LOW,  and  com- 
paratively little  to  the  HIGH  or  anti- 
cyclone.    For  we  are  now  beginning  to 
understand  that  while  there  may  seem 
at  first   to   be  nothing  specially  note- 
worthy about  a  mass  of  air  where  the 
pressure  varies  from  1020  to  1040  kilo- 
bars,  that  is,  2  to  4  per  cent  above  a 
standard  atmosphere,  with  isobars  ir- 
regularly   curved    and    feeble    surface 
winds,  yet  the  anticyclone  is  more  im- 
portant than  the  cyclone  in  determining 

[35] 


WIND        AND        WEATHER 

weather  sequence;  for  the  progressive 
motion  of  the  cyclone  depends  largely 
upon  the  strength  of  the  anticyclone. 

*     *     *     * 

OCEAN  STORMS 

Sir  Napier  Shaw,  who  has  written 
much  on  the  weather  of  the  British 
Isles,  may  be  quoted  here. 

"Anyone  who  is  interested  in  the 
weather  is  always  on  the  lookout  for 
'lows'  and  is  very  keen  to  know 
whether  he  is  going  to  be  on  the  south 
of  the  centre  or  the  north  of  it.  He  is, 
of  course,  interested  in  the  anticy- 
clone too,  because  as  long  as  an  anti- 
cyclone is  there,  there  cannot  be  a  de- 
pression; but  it  is  the  depression  which 
has  the  life  and  movement  about  it, 
giving  it  a  claim  to  the  attention  of 
everybody  who  wants  to  know  what 
the  weather  and  its  changes  are  going 
to  be. 

[36] 


•  1 


g 

o 

C/3 


WIND        AND        WEATHER 

"This  has  been  recognized  from  the 
very  earliest  days  of  weather  maps 
with  isobars.  The  depressions  which 
pass  over  our  shores  (Great  Britain) 
mostly  come  from  the  west.  Some  of 
them  come  all  the  way  from  America; 
one  or  two  have  been  traced  from  the 
west  coast  of  Africa  and  so  have 
crossed  the  Atlantic  twice,  first  to  the 
westward  and  then  to  the  eastward. 
Some  have  come  all  the  way  from  a 
sort  of  parent  'low'  in  the  North 
Pacific  Ocean.  So  general  is  the  tend- 
ency for  'lows'  to  go  eastward 
that  it  was  thought  at  one  time,  par- 
ticularly by  the  'New  York  Herald,' 
that  their  departure  from  the  American 
Coast  and  subsequent  arrival  on  our 
own  shores  could  be  notified  by  cable, 
and  we  (the  British)  might  thus  be 
forewarned  of  their  approach,  some 
three  or  four  days  in  advance.  The 
attempt  was  made  by  the  'New  York 

[39] 


WIND        AND        WEATHER 

Herald'  acting  in  co-operation  with 
the  Meteorological  Offices  of  the 
United  Kingdom  and  France.  But  a 
depression  keeps  to  no  beaten  track; 
it  has  as  many  paths  for  its  centre  as 
there  are  lines  in  a  bundle  of  hay. 
Though  groups  can  be  picked  out 
there  are  many  strays,  and,  moreover, 
the  depression  changes  its  shape  and 
intensity  while  it  travels,  so  that  if 
you  lose  sight  of  it  for  a  day  you  can- 
not be  at  all  sure  of  its  identity." 


TRANSCONTINENTAL  STORMS 

If  there  is  so  much  uncertainty  in 
forecasting  the  path  of  a  disturbance  at 
sea,  how  much  more  uncertain  must  it 
be  on  land?  Elaborate  statistics  of  the 
average  daily  movement  of  various 
types  of  storms  have  been  officially  pub- 
lished. The  average  speed  of  storms 
[40] 


H 

I 


WIND        AND        WEATHER 

(not  wind  speeds)  across  the  United 
States  is  ii  metres  per  second  or  25 
miles  an  hour.  Storms  travel  more 
rapidly  in  winter  than  in  summer,  about 
half  again  as  fast;  that  is,  summer 
storms  travel  20  miles,  and  winter  storms 
30  miles,  an  hour. 

The  paths  vary  widely;  from  the  Gulf 
storms  moving  northeast  and  West 
Indian  hurricanes  recurving  on  the 
southern  coast,  to  the  storms  from 
Alberta  and  the  west  which  move  south 
and  east.  Ten  types  of  storms,  classi- 
fied according  to  the  place  of  origin,  are 
recognized  by  the  official  forecasters  of 
the  United  States.  These  are  North 
Pacific,  Alberta,  Northern  Rocky  Moun- 
tain, Colorado,  Central,  South  Pacific, 
Texas,  East  Gulf,  South  Atlantic  and 
West  Indian  Hurricanes.  A  better 
nomenclature  would  be  (i)  Alberta,  (2) 
Washington,  (3)  Kootenay,  (4)  Utah, 
(5)  Kansas,  (6)  California,  (7)  Texas, 

[43] 


WIND        AND        WEATHER 

(8)    Louisiana,    (9)    Florida,    and    (10) 
Hurricanes. 


HURRICANES 

Type  10  is  the  general  class  of  tropical 
storms  occurring  chiefly  in  the  summer 
and  fall  which,  drifting  west,  slowly 
work  northward.  Similar  storms  are 
the  typhoons  and  baguios  of  the  East 
Indian  and  China  Seas. 

The  path  and  point  of  recurvature 
will  be  determined  by  the  position  of  the 
Bermuda  Hyperbar,  that  is,  the  seasonal 
anticyclone  of  the  Atlantic.  This  ac- 
counts for  the  swinging  east  and  north 
of  these  tracks  as  the  season  progresses; 
for  the  hyperbar  is  slowly  displaced  east, 
the  maximum  displacement  occurring  in 
September. 

Individual  anticyclones  also  influence 
individual  hurricanes.  Thus  a  hurri- 
cane passing  west  over  Havana,  will  go 

[44] 


BASE    MAP    BY    GOODE 

FIG.  8.     ALL  STORMS  LEAD  TO  NEW  ENGLAND 


WIND        AND        WEATHER 

farther  west  if  a  vigorous  "high"  is 
spreading  southeast  over  the  Gulf  States. 
And  when  this  "high"  passes  seaward, 
the  hurricane  will  work  around  the 
southwest  quadrant  of  the  "high,"  re- 
curving and  moving  northeast. 
*  *  *  * 

STORM  RENDEZVOUS 

Altho  storms  originate  or  are  first  de- 
tected in  nine  different  sections,  it  is  a 
fact  worth  mentioning  that  they  all 
•  leave  the  United  States  in  the  vicinity 
of  New  England  or  Nova  Scotia.  Some 
of  the  southern  depressions  starting  near 
the  coast,  pass  to  sea  south  of  New 
York,  but  in  general  an  observer  stand- 
ing on  Plymouth  Rock  can  virtually 
encompass  within  a  radius  of  500 
kilometres,  300  miles,  the  paths  of 
ninety  per  cent  of  the  storms  that 
traverse  the  country. 

Thus  a  storm  that  originates  in  Texas 
(7)  will  probably  pass  close  to  Cape  Cod. 

[47] 


WIND        AND        WEATHER 

Likewise,  types  (3)  and  (5);  while  the 
other  types  may  pass  a  little  to  the  north 
or  south.  See  Chart,  Paths  of  Storms. 


STORM  PATHS 

Forecasting  then  would  seem  to  be 
very  easy;  for  one  would  only  have  to 
know  the  place  of  origin  of  the  storm 
and  the  rate  of  travel,  to  foretell  exactly 
the  time  of  arrival.  Unfortunately 
these  are  only  the  average  paths;  and  as 
with  most  mean  values,  represent  a  value 
not  often  experienced  in  fact.  These 
paths  then  are  not  paths  which  any 
given  storm  will  follow.  One  must  re- 
call the  story  of  the  operating  surgeon 
who  gave  the  average  age  of  his,  pa- 
tients in  the  operating  room  as  35. 
There  were  but  two  patients,  one  69 
years  old  and  the  other  i  year  old. 

As  a  matter  of  fact  the  path  of  any  in- 
dividual depression  depends  upon  sever- 

[48] 


Jfe. 


£ 

(4 


WIND        AND         WEATHER 

al  factors,  some  of  which  are: — the  pre- 
vailing eastward  drift  of  the  air;  the  ex- 
tent and  motion  of  some  anticyclone 
advancing  before  the  "LOW";  the  dura- 
tion and  speed  of  relatively  dry  cold 
tongues  of  air  from  the  north;  and  the 
supply  of  water  vapor  brought  from 
southern  waters  by  south  winds.  A 
depression  can  make  little  headway  if  to 
the  north  or  east  the  normal  path  is 
blocked  by  what  is  known  as  a  stagnant 
"HIGH."  So  therefore,  if  the  anti- 
cyclone is  a  slow  mover,  a  Texas  storm, 
which  would  normally  pass  not  far 
from  southern  New  England,  may  be 
deflected  farther  north  than  when  the 
HIGH  moved  rapidly  east.  So  too, 
with  the  storms  which  originate  in  the 
western  part  of  the  country.  A  slow 
moving  HIGH  will  prevent  the  LOW 
following  it,  from  moving  east  at  a  nor- 
mal rate  along  the  usual  path. 

Anticyclones  then,  are  the  real  weather 

[51] 


WIND        AND        WEATHER 

controls.  "There  are  various  types,  but 
all  drift  from  the  north  or  west.  Oc- 
casionally they  enter  the  country  from 
the  Pacific,  but  the  great  majority  come 
from  Alberta  and  move  leisurely  south- 
east, often  reaching  the  South  Atlantic 
States;  but  more  frequently  recurving 
and  passing  to  the  north. 


STAGNANT  HIGHS 

HIGHS  are  sometimes  reinforced  and 
this  results  in  what  is  called  a  stagnant 
HIGH.  A  good  illustration  of  such  a 
slow  moving  HIGH  and  its  consequences 
occurred  during  the  last  week  of  Jan- 
uary, 1922. 

A  surge  of  cold  air  from  Alberta  or 
farther  north  reached  the  international 
boundary  January  2ist  and  spread 
slowly  eastward,  reaching  the  Great 
Lakes  on  the  24th  and  the  St.  Lawrence 
Valley  two  days  later.  Then  seemingly 

[52] 


WIND        AND         WEATHER 

it  halted  or  moved  slowly  westward,  re- 
trograding. In  three  days,  that  is,  on 
the  29th,  the  centre  of  the  HIGH  was 
apparently  500  miles  west  of  where  it 
had  been  on  the  27th.  After  the  29th 
it  followed  a  normal  track,  moving  slow- 
ly southeast,  reaching  the  Atlantic  near 
Long  Island. 

Meanwhile  a  depression  on  the  south 
coast  of  Texas  on  the  25th,  moved 
across  the  Gulf  of  Mexico,  passing  over 
Southern  Florida  on  the  2yth  and  ad- 
vanced steadily  northeast,  reaching  Cape 
Hatteras  in  24  hours.  Owing  to  the 
presence  of  the  anticyclone  referred  to 
above,  the  depression  recurved  off 
Hatteras.  The  result  was  a  memorable 
snow  storm  in  Northern  Virginia  and 
Maryland.  At  8  p.m.  January  27th, 
there  had  been  a  fall  of  5  cms.  (2 
inches).  Within  the  following  twenty 
hours  the  average  depth  in  the  city  of 
Washington  was  66  cms.  (26  inches). 

[53] 


WIND        AND        WEATHER 

The  weight  of  the  snow  caused  the  col- 
lapse of  the  roof  of  the  Knickerbocker 
Theatre  and  the  death  of  97  persons. 

The  total  snowfall   in  various  coast 
cities  was: 

Raleigh 24  cms.* 

Richmond 48  <    " 

Washington. 71 

Baltimore 67 

Wilmington 46 

Philadelphia.  ......  31 

Trenton 27       " 

New  York 18       " 

New  Haven 8 

Boston i 

*Note:    To  convert  to  inches  multi- 
ply by  0.4. 

The  table  shows  clearly  how  the  snow 
was  formed.  On  the  east  side  of  the 
LOW  a  stream  of  air,  relatively  warm, 
carried  a  load  of  water  vapor,  approxi- 
mately 13  grams  in  each  cubic  metre. 
[54] 


BASE   MAP   BY   GOODE 


FIG.  10.     PATHS  OF  HIGH  AND  Low,   GREAT    SNOW 
STORM  OF  JANUARY  27-28,  1922 


WIND        AND         WEATHER 

This  current  was  steered  around  the 
north  side  of  the  LOW  and  met  the 
north-northeast  wind.  Under  the  new 
conditions  the  air  saturated  could  hold 
only  2  or  3  grams;  and  so  condensation 
and  heavy  precipitation  resulted/  The 
region  of  maximum  snowfall  was  near 
Washington,  and  it  will  be  seen  that 
there  is  a  proportional  decrease  north 
and  south.  The  snowfall  at  Washington 
was  the  heaviest  ever  known  at  that 
city. 

Unlike  most  storms,  there  was  no 
strong  cold  northwest  wind  blowing 
into  the  depression.  The  temperature 
rose  slowly.  It  was  less  a  contrast  of 
winds  than  a  steady  slow  outward  push 
of  the  anticyclone,  and  the  consequent 
turning  of  the  path  of  the  cyclone  east- 
ward. 


[57] 


LAWS  OF  FORECASTING 

Buys  Ballot's  Law. 

"If  you  stand  with  your  back  to  the 
wind  the  pressure  decreases  toward  your 
left,  and  increases  toward  your  right." 

For  navigators,  this  law  is  more 
generally  expressed  in  the  words  of 
the  Hydrographic  Office  on  "Cyclonic 
Storms." 

"Since  the  wind  circulates  counter- 
clockwise in  the  northern  hemisphere, 
the  rule  in  that  hemisphere  is  to  face  the 
wind,  and  the  storm  centre  will  be  at  the 
right  hand.  If  the  wind  traveled  in  ex- 
act circles,  the  centre  would  be  eight 
points  (90  degrees)  to  the  right  when 
looking  directly  in  the  wind's  eye.  But 
the  wind  follows  a  more  or  less  spiral 
path  inward  which  brings  the  centre 
from  eight  to  twelve  points  (90  to  135 
degrees),  to  the  right  of  the  wind.  The 
centre  will  bear  more  nearly  eight  points 
from  the  direction  of  the  lower  clouds 
than  from  the  surface  wind." 
[58] 


I 
I 


WIND        AND        WEATHER 

The  law  given  on  the  preceding  page 
is  named  after  C.  H.  D.  Buys  Ballott,  a 
Dutch  meteorologist.  It  was  an- 
nounced in  a  paper  published  in  the 
Comptes  rendus  in  1857.  Two  American 
writers  on  the  Winds,  J.  H.  Coffin -and 
William  Ferrell,  had  however  earlier 
found  the  law  to  hold. 


While  most  of  us  study  storms  from  a 
window  at  home  and  are  not  called  upon 
to  handle  a  ship  in  a  storm,  yet  it  may 
not  be  out  of  place  to  include  here  the 
diagram  of  the  winds  in  an  ideal  storm 
and  give  the  rules  for  maneuvering. 
See  Figure  12.  The  Winds  in  an  Ideal- 
ized Storm.  The  rules  apply  only  to 
storms  in  the  northern  hemisphere. 

"Right  or  dangerous  semicircle,, — Steam- 
ers: Bring  the  wind  on  the  starboard 
bow,  make  as  much  way  as  possible,  and 
if  obliged  to  heave-to,  do  so  head  to  sea. 

[61] 


WIND        AND        WEATHER 

Sailing  vessels:  Keep  close-hauled  on 
the  starboard  tack,  make  as  much  way 
as  possible,  and  if  obliged  to  heave-to, 
do  so  on  the  starboard  tack. 

Left  or  navigable  semicircle, — Steam 
and  sailing  vessels:  Bring  the  wind  on 
the  starboard  quarter,  note  the  course 
and  hold  it.  If  obliged  to  heave-to, 
steamers  may  do  so  stern  to  sea;  sailing 
vessels  on  the  port  tack. 

On  the  storm  track  in  front  of  center, — 
Steam  and  sailing  vessels:  Bring  the 
wind  two  points  on  the  starboard 
quarter,  note  the  course  and  hold  it,  and 
run  for  the  left  semicircle,  and  when  in 
that  semicircle  manoeuvre  as  above. 

On  the  storm  track,  in  rear  of  center, 
—Avoid  the  center  by  the  best  practi- 
cable route,  having  due  regard  to  the 
tendency  of  cyclones  to  recurve  to  the 
southward  and  eastward. 


[62] 


FROM  HYDROGRAPHIC  OFFICE 

FIG.  12.    THE  WINDS  IN  AN  IDEALIZED  STORM 


WIND  AND  ALTITUDE 

The  law  of  the  turning  of  the  wind 
with  altitude. 

A  casual  observation  of  the  lower 
clouds  where  no  means  of  measuring 
small  angles  is  available  will  not  usually 
show  any  difference  between  the  motion 
of  the  clouds  and  the  surface  wind;  but 
with  the  upper  clouds  the  case  is  differ- 
ent, and  one  readily  detects  a  difference. 

Several  thousand  observations  with 
various  agencies,  such  as  kites  and 
pilot  balloons  and  more  especially  meas- 
urements made  with  theodolites  and 
nephoscopes,  show  that  there  is  a  defin- 
ite twist  to  the  right  with  elevation. 
The  amount  of  the  deflection  is  shown  in 
Figure  13.  Turning  of  the  Wind  with 
Altitude.  Here  the  average  yearly  val- 
ues are  given  for  directions  and  veloci- 
ties. Thus  if  the  mean  wind  direction 
at  Blue  Hill  is  from  a  point  a  little  to  the 
north  of  west,  306  grads  or  275  degrees, 
and  the  mean  velocity  7  metres  per 
[65] 


WIND        AND        WEATHER 

second;  the  clouds  at  1000  metres  eleva- 
tion will  move  from  312  or  280  degrees 
and  at  a  speed  of  approximately  n 
metres  per  second  (24  miles  an  hour). 

These  however,  are  average  values. 
In  individual  cases  the  difference  be- 
tween surface  winds  and  stratus  clouds 
may  be  considerably  greater.  It  may 
be  as  much  as  180  degrees;  that  is,  the 
cloud  may  move  directly  opposite  to  the 
wind.  In  general  there  will  be  a  differ- 
ence of  10  to  20  degrees. 

*     *     *     * 
WIND  AND  RAIN 

The  law  of  wind  direction,  approxi- 
mate cooling  and  rain. 

When  the  lower  clouds  are  moving 
from  the  north  or  northwest,  without 
sharply  defined  edges,  the  LOW  is  east 
or  northeast  of  the  observer;  and  rain  or 
snow  is  not  likely  unless  there  is  a  rapid- 
ly falling  temperature. 

[66] 


I         t 

^•^^^^ 


FIG.  13.     TURNING  OF  WIND  WITH  ALTITUDE 


WIND        AND        WEATHER 

When  a  stream  of  warm  air  with  a 
high  absolute  humidity  flows  north  on 
the  east  side  of  a  LOW,  and  a  cold  north- 
west wind  follows  quickly  after  the  LOW, 
rain  or  snow  may  be  expected. 

Any  rapid  chilling  of  warm,  moist  air 
produces  cloudiness  and  rain  or  snow; 
but  a  cold  stream  blowing  into  a  warm 
area  will  not  produce  as  much  rain  as  a 
warm  stream  blowing  into  a  cold  area. 


[69] 


DURATION  OF  WIND 

The  average  duration  of  wind  from 
various  directions  is  as  follows: 

From  the  north  about  16  hours  each 
week;  from  the  northeast,  the  same; 
from  the  east,  n  hours;  from  the  south- 
east, 10  hours;  from  the  south,  24  hours; 
from  the  southwest,  27  hours;  from  the 
west,  33  hours;  and  from  the  northwest 
31  hours. 

During  an  individual  disturbance 
lasting  about  36  hours,  we  may  have  8 
hours  of  southwest  wind;  4  hours  of  west 
wind,  backing  during  the  next  4  hours  to 
south;  2  hours  of  south  wind;  2  hours  of 
southeast  wind;  2  hours  of  east  wind;  8 
hours  northeast  wind  and  4  hours  north 
wind,  2  hours  northwest,  when  it  may 
be  considered  that  a  new  pressure  dis- 
tribution prevails. 

The  above  values  hold  only  for  a 
storm  moving  with  normal  velocity. 
LOWS  are  often  blocked  by  slow  moving 
HIGHS  in  advance.  In  such  cases  the 
duration  of  east  winds  is  greater. 
[70] 


THE  WINDS  OF  A  YEAR 

The  following  table  shows  the  marked 
increase  in  the  prevalence  of  northwest 
and  west  winds  during  winter  months, 
the  decrease  in  north  winds  during  July, 
the  increase  in  northeast  winds  in  May, 
also  in  east  winds;  the  increase  of  south 
and  southwest  winds  in  July;  and  the 
falling  off  of  southeast  winds  in  Decem- 
ber. See  Table,  page  72. 

In  cities  near  the  Atlantic  Coast,  a 
continuance  of  northeast  wind,  espe- 
cially in  the  fall  and  winter  months,  re- 
sults in  frequent  altho  not  necessarily 
heavy  rains.  On  the  other  hand  a 
period  of  continued  northwest  and  west 
wind  is  a  dry  period. 

In  summer,  southeast  and  east  winds 
bring  fog  and  cooler  weather;  while 
southwest  winds  are  favorable  for  the 
development  of  thunderstorms. 


[71] 


§ 
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c 

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£ 


JD 
PQ 


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Q  OOOS'-OTj-OiOCOCO 

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*-1     CSOO 


O      i-i      COTt-COOO 

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il'lol 


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[72] 


JKJV.VK 


ffjr.E. 


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,£.S.E. 


FIG.  14.     VELOCITY  OF  SUMMER  AND  WINTER  WINDS 
IN  METRES  PER  SECOND 


THE  SEA  BREEZE 

When  the  weather  has  been  clear  and 
moderately  warm  for  two  or  more  days, 
and  the  winds  are  light  and  variable, 
there  may  occur  on  the  third  day  a 
moderate  wind  from  the  east,  known  as 
the  sea-breeze.  This  occurs  during  anti- 
cyclonic  conditions.  Preceding  the  sea- 
breeze,  the  winds  are  very  light,  there 
are  no  clouds,  and  the  temperature  rises 
rapidly  during  the  forenoon.  This  heat- 
ing is  due  to  a  slow  dynamic  compression 
as  the  air  slowly  descends  and  the  sur- 
face air  does  not  flow  away.  There  is  no 
cooling  because  there  is  no  evaporation 
due  to  air  movement.  The  absolute 
humidity  is  low,  often  less  than  ten 
grams  per  cubic  metre.  Cumulus  clouds 
do  not  form  because  there  is  no  uplift 
of  the  lower  air  and  consequently  no 
chance  for  condensation  of  whatever 
water  vapor  may  be  present.  No 
thunder-heads  form  notwithstanding  the 

[75] 


WIND        AND        WEATHER 

heat.  The  heat,  while  dry,  is  neverthe- 
less extremely  trying  to  men  and  animals. 
Relief  comes  in  the  early  hours  of  the 
afternoon  by  the  arrival  of  the  sea- 
breeze. 

The  usual  explanation  of  the  origin  of 
the  sea-breeze  is  that  the  land  being  ex- 
cessively warm,  the  air  over  a  relatively 
cool  ocean  moves  in  to  take  the  place  of 
the  warm  and  therefore  lighter  air,  which 
it  is  assumed  has  risen.  Unfortunately 
for  this  explanation,  the  air  over  the 
land  has  not  risen;  but  on  the  contrary 
is  falling  slowly.  Again  the  sea-breeze 
does  not  begin  at  the  place  where  the 
temperature  contrast  is  greatest,  namely, 
just  inside  the  shore  line;  but  comes  in 
from  the  sea.  Nor  does  the  flow  extend 
far  inland,  which  would  be  the  case  if 
there  were  up-rising  currents.  The  sea- 
breeze  is  very  shallow,  generally  not  ex- 
tending upward  more  than  200  metres, 
and  often  not  above  100  metres.  It 
[76] 


WIND        AND        WEATHER 

does  not  penetrate  far  inland,  as  a  rule 
not  more  than  15  kilometres,  9  miles. 

The  sea-breeze  is  probably  caused  by 
a  slow  descent  of  dry,  warm  air,  on  an  in- 
cline sloping  from  northeast  to  south- 
west. As  it  reaches  the  surface  it  is 
twisted  more  to  the  right;  that  is,  be- 
comes an  east  wind.  It  carries  inland 
with  it  some  of  the  air  over  the  ocean 
which  is  much  cooler  and  heavily  satu- 
rated. 


[77] 


MUGGY  DAYS 

There  are  certain  days,  more  notice- 
able in  summer  than  at  other  times,  when 
the  air  is  heavily  laden  with  water  vapor; 
and  there  is  little  or  no  cooling  of  the 
body  due  to  evaporation.  We  perspire 
freely  but  as  the  sweat  does  not  evap- 
orate, there  is  a  constantly  increasing 
amount  of  water  on  the  skin. 

It  is  not  altogether  a  question  of  tem- 
perature, for  another  day  may  have  as 
high  or  even  higher  temperature.  It  is 
essentially  a  matter  of  ventilation.  On 
muggy  days  we  are  somewhat  in  the 
condition  of  the  unfortunate  prisoners 
in  the  Black  Hole  at  Calcutta.  They 
did  not  die  by  poisoning,  as  has  generally 
been  accepted,  that  is,  lack  of  sufficient 
oxygen  and  an  excess  of  carbon  dioxide; 
but  because  they  were  unable  to  keep 
the  skin  sufficiently  cool.  There  was 
no  ventilation;  no  movement  of  the  air 
and  the  body  became  over-heated  and 
exhaustion  followed.  No  matter  how 
[78] 


o 

£ 


WIND        A^TD        WEATHER 

much  water  there  may  be  on  the  skin  if 
the  surrounding  space  is  saturated,  one 
feels  oppressed.  A  vigorous  fanning  of 
the  air  helps  evaporation  and  cools  us. 
That  is  why  a  brisk  northwest  wind  routs 
a  muggy  condition. 

#  *  *  # 
CASTILIAN  DAYS 
John  Hay  wrote  of  such  days  spent 
in  Spain.  We  who  live  in  a  land  where 
the  winds  are  more  boisterous,  occasion- 
ally experience  what  we  call  a  perfect 
day.  Such  days  have  easterly  winds  of 
two  metres  per  second  or  less  than  five 
miles  an  hour.  The  temperature  is 
midway  between  freezing  and  normal 
body  temperature  or  about  70°  F.  The 
relative  humidity  is  approximately  75% 
and  the  absolute  humidity  12  grams  per 
cubic  metre.  The  table  on  page  72 
explains  the  paucity  of  perfect  days. 
The  gusty,  boisterous  winds,  Skiron  and 
Zephyros,  blow  too  frequently. 

[81] 


WIND        AND        WEATHER 

Perhaps  certain  of  our  national  char- 
acteristics may  be  traceable  to  this  flow 
of  the  air  and  our  climatic  environ- 
ment. 


[82! 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


AN  INITIAL  FINE  OF  25  CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  5O  CENTS  ON  THE  FOURTH 
DAY  AND  TO  $1.OO  ON  THE  SEVENTH  DAY 
OVERDUE. 


DEC 


JUN    3 


DEC    21937 


27- 


AUG  25  1939 


SEP 


V'v' 

OCT  13  tgjj^ 

DEC  17^946 

jjj? 

LD  21-100m-7,'33 

500823 


o,c 

M2> 


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